1. Field of the Invention
The present invention relates to a filter for a display device having an antireflection property superior in stain resistance, scratch resistance, processing resistance, etc. and further relates to a filter able to be used as the front panel of a CRT.
2. Description of the Related Art
When viewing an object through a transparent material, it is bothersome if the reflected light is strong and the reflected image is clear. For example, in eyeglass lenses, "ghosts", "flares", and other reflected images occur and give an unpleasant feeling to the eye. Further, in telescopes etc., a problem occurs that the object viewed cannot be discerned due to the light reflected on the surface of the glass.
In the past, to protect against reflection, a substance having a reflectance different from the substrate has been coated on the surface by vacuum deposition etc. In this case, to bring out the maximum antireflectance effect, it is known to be important to properly select the thickness of the substance covering the substrate.
For example, selection of the optical thickness of the substance of the reflectance lower than the substrate to be 1/4 of the wavelength covered or an odd multiple of the same is known to give the smallest reflectance, that is, an extremely large transmittance.
Here, the optical thickness is given by the product of the reflectance of the coated shaped material and the thickness of the coating. Further, it is possible to form a plurality of layers of antireflectance films. Several proposals have been made regarding the selection of the thickness in this case (Kagaku Gijutsu Contact (Optical Technology Contacts), Vol. 9, No. 8, p. 17 (1971)).
On the other hand, the methods for forming antireflection films comprised of multiple layers satisfying the condition of the optical thickness using a liquid composition are described in Japanese Unexamined Patent Publication (Kokai) No. 58-46301, Japanese Unexamined Patent Publication (Kokai) No. 59-49501, and Japanese Unexamined Patent Publication (Kokai) No. 59-50401. In recent years, the advantages of light weight, safety, ease of handling, and the like have been used to produce and commercialize optical products using a plastic substrate and having an antireflectance. Further, most use configurations of films having a silicon dioxide surface layer film.